Impact of Artificially Induced Respiratory Deficient Yeast on Beer Flavor and Fermentation

Respiratory deficient cells or "petites" are the most common type of mutation found in brewing yeast. High levels of petites are known to contribute to unwanted flavors in beer along with yeast flocculation problems during fermentation. However, a minimal amount is known regarding the impact of petites when present at naturally occurring frequencies. Accordingly, this study investigated if petites, which are present at low frequencies, affect beer flavor and fermentation profiles. Laboratory [20 mL] fermentations were undertaken with yeast that contained a range of petite populations 3.7, 5.1, 8.7, and 10.8%. During fermentation, the yeast in suspension, wort density, and alcohol were monitored. At the end of the fermentation, the beer was analyzed for volatile flavor compounds. Correlations between petite levels and levels of vicinal diketones, acetate esters, and medium chain fatty acid (MCFA) ethyl esters existed. Higher alcohol levels were unchanged (propan-1-ol, 3-methyl butanol, 2-methyl butanol, and isobutanol) with increasing levels of petite concentrations. Similarly, the yeast in suspension behavior and the change in wort density attenuation between the control and petite enriched fermentations were not significantly different (P> 0.05). This study suggests that low concentrations of petites in the pitched yeast would not be detectable in the final product characteristics.